1. Field of the Invention
This invention relates to devices for measuring the shape of a human foot. More particularly, this invention relates to devices which measure the shape of the foot by producing a moire fringe pattern on the underside of the foot while the foot is bearing weight, and then analyze that pattern to determine the foot shape.
2. Description of Related Art
Previous devices for measuring the shape of a foot have generally employed one of two distinct methods of operation.
The first method involves mechanically measuring the shape of the foot by making physical contact between the sides of the foot and a probe. For example, the common foot-size measurement tool found in most shoe stores generally includes a pair of blocks, one of which is fixed and one of which slides along a distance scale between them. The heel of the foot is placed in contact with the fixed block and the sliding block is pushed into contact with the toes, after which the foot length can be read from the scale. Devices employing physical contact with the foot, however, often produce measurements which vary, even when measuring the same foot, due to the compressibility of the foot tissue and the difficulty of determining the exact moment of contact.
The second method involves placing the foot to be measured over an array of detectors sensitive to the presence or absence of light. The foot is then illuminated from above and an outline of the foot is determined by scanning the detectors An example of this type of device is found in U.S. Pat. No. 4,538,353 issued to Gardner and the related U.S. Pat. No. 4,604,807 issued to Gardner et al.
This method is an improvement over the first one in that it produces a complete foot outline, not just a single linear measurement of width or length. It also requires no physical contact with the sides of the foot which improves the repeatability of the measurements. However, it suffers from several inaccuracies of its own. The human foot does not have sides which are exactly square and perpendicular to its sole. Instead, they are curved and flare out from the portion of the sole in contact with the supporting surface. In the arch region, the sole of the foot may not be in contact with the supporting surface for a substantial distance inwards from the edge of the foot.
This three-dimensional nature of the foot permits light to leak under the edges of the foot activating the detectors and resulting in a detected foot outline which is much smaller than the actual foot. The extent of this undersizing varies depending on the foot being measured. One foot may make close contact with the supporting surface around its perimeter, or may have little or no arch thereby covering more detectors than another foot. Undersizing may also occur if the foot is not measured under load with the normal body weight applied.
This second method also suffers from problems with shadows cast by the foot and leg because of the difficulty of providing collimated illumination from directly above the foot.
Such prior art measuring devices have generally been used to measure the foot for shoe size and width. Many times, however, one wants to measure a foot in order to construct an orthotic insert for a shoe to balance the foot to a plantigrade position.
Such inserts have previously been prepared by taking an impression of the foot in a material that permanently deforms to follow the contours of the foot, thereby producing a mold. The insert is then produced either directly in that mold or on the exterior of a second mold produced by taking a positive casting from the first mold. However, small changes in the angle of insertion of the foot into the deformable media can result in an incorrect mold, and an incorrectly shaped insert. These problems are not present when the foot is measured with the pedotopography apparatus of the present invention.
Accordingly, one object of the present invention is to provide a pedotopography apparatus which is capable of measuring dimensions of the foot at an elevation above the plane of the supporting surface while the foot is under its normal standing load.
A second object of the invention is to provide a pedotopography apparatus which is capable of measuring the arch and other features of the foot within the perimeter of the foot.
Another object of the invention is to provide a pedotopography apparatus which can record images of the foot for subsequent review and analysis.
A further object of the invention is to provide a pedotopography apparatus which can produce a foot "signature" of measured dimensions of or locations on a foot and compare that signature to a database of previously measured feet to select an appropriately shaped shoe or insert.